"You do realise that the only thing between us and the jaws of a great white shark is a piece of string?" observed my fellow passenger. Until then I had been happy lounging on the safety net below the bowsprit of Royal Clipper, photographing the dolphins riding the bow wave beneath us. I put my camera away sharpish and clambered back on deck.

I had boarded Royal Clipper the day before, in Grenada, for a five-day tour of the Grenadines. The 227-passenger Royal Clipper is the world's largest five-masted ship, its small passenger count meaning you get to know fellow travellers: the two minutes it takes to walk around the ship – along elegant corridors and up and down Edwardian-style staircases on its luxury cruises – means you can't fail to meet and talk to everyone else on its Caribbean cruises.

The first night found me at the indoor-outdoor Tropical Bar, the place everybody met up each night and where the ice between guests melted quickly. A local steel band played and as the sun set over the roof tops and fort of the old town the ambience for the trip was set.

Next morning I was up early. To be on the deck of a cruise ship at sunrise is often memorable, but on the Royal Clipper the occasion is given extra lustre by that lovely early light catching the sails. Then it was off to Mario, the ship's marine biologist, for a dolphin-watching session: you can watch as many TV wildlife programmes as you like but it's not until you see the ocean seething with dolphins that you really appreciate these magnificent creatures.

Our first port of call was the Tobago Cays, a beautiful and uninhabited group of islands. From the moment our tender landed on the pristine white sands I knew we were somewhere special. The temptation was just to flop on the beach, but I made myself take the track on the eastern end of the beach to the other side of the island. The path brought me to a lagoon of clear water, iridescent green and yellow birds and a deserted beach where I half expected to find Robinson Crusoe or Captain Jack Sparrow walking towards me. I had borrowed snorkelling gear from the ship so spent a pleasant hour looking for "sea goats" – the local name for turtles.

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Life on board was relaxed, but the ship maintains a smart-casual dress code. Beach or resort wear on deck during the day and smarter during the evening (though not dinner jackets), with one gala night on each cruise where people dress up a little more. As part of the casual approach, guests can dine when they like and with whom they like.

The next stop was St Vincent and its capital Kingstown, busy with men loading and unloading lorries, fruit and fish markets and impromptu stalls on street corners. Respite from the bustle came in the cloisters and gardens of the two cathedrals.

In complete contrast, that afternoon found us anchored off the tiny island of Bequia. The wooden jetty, the small church with names of 18th-century British settlers set into its stained glass, and the children with their tartan school dresses (10 per cent of today's population is of Scottish descent) on their way home after netball practice all seemed to take us back to a bygone age; even the pelicans and frigate birds circling above as we waited to return to the ship added to the feeling.

The beauty of this cruise was that each island we visited had its own character, none more so than Martinique, as much a part of France as Berkshire is of Great Britain.

The euro is the currency but Fort-de-France has the air of a slightly rundown New Orleans, its spice market an island of cinnamon, rum and coconuts in a sea of narrow streets lined with pastel-coloured houses and slow-rusting balconies.

The islands we visited were tremendous, but what makes Royal Clipper unique is that you have the opportunity, should you so wish, to become part of the crew and get under the skin of this magnificent vessel.

In my short time on board I helped the crew put up the sails, learned various knots, watched as the captain talked us through turning her through 360 degrees, held the wheel, learned about navigation and even helped swab down the decks. Climbing the rigging (attached to a winch) to the crow's nest was also an experience.

The Royal Clipper may not offer the glamorous organised entertainment found on the bigger ships but I didn't miss it. To be at sea at night on a sailing ship is entertainment in itself – one night I decided to join many of my fellow passengers who were sleeping on the deck. Lying back on my sun lounger I watched the riggers high above on the yard arms, adjusting the sails. Running along the spars they were silhouetted against the moonlit sky and for one brief, magical moment I was with Captain Cook in Tahiti.

It was also perhaps the highlight of the trip – though canoeing, diving, swimming, water-skiing from the ship at anchor were memorable, as was snorkelling off the coast of St Lucia amid thousands of multicoloured fish and photographing the magnificent spectacle of the ship under full sail at sea from a tender. But that brief time under the stars, when I could truly imagine what it must have been like when these magnificent vessels ruled the waves, was a memory beyond compare.